This application claims the priority of Korean Patent Application No. 10-2004-0011321, filed on Feb. 20, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to a sensitivity enhanced biomolecule field effect transistor (FET), and more particularly, to a biomolecule FET enhancing sensitivity when detecting a biomolecule by improving a structure of a transistor-based biomolecule FET.
2. Description of the Related Art
Among sensors designed to detect a biomolecule using an electrical signal, there is a TR-based biosensor having a transistor structure. The biosensor is manufactured through a semiconductor manufacturing process, and has advantages in that the electrical signal is quickly converted and inoculation of IC and MEMS is simplified. However, since the biosensor has a lower confidence in a ratio of signal-to-noise (SNR) which is an important variable in the biosensor, various efforts to improve the ratio are in progress.
To detect a biological reaction using an FET is disclosed in U.S. Pat. No. 4,238,757 (1980), in which it refers to a biosensor for detecting a current and claims protein among biomolecules, and which a reaction between an antigen and an antibody is detected by use of a change in a semiconductor inversion layer due to a variation of a surface-charge concentration. U.S. Pat. No. 4,777,019 (1986) discloses an FET for detecting a level of hybridization between biological monomers attached onto a surface of a gate and complementary monomers. U.S. Pat. No. 5,846,708 (1998) discloses a method for detecting a level of hybridization using light attenuation caused by a biomolecule provided with a charged coupled device (CCD). U.S. Pat. Nos. 5,466,348 and 6,203,981 disclose to improve the SNR using a thin film transistor (TFT) associated with a circuit.
The TFT, it can lower the costs in relation to a transistor formed on a silicon substrate. Also, it is possible to manufacture an array of chips by enlarging a surface area of the substrate to improve a degree of integration. Use of the FET as the biosensor results in an economical, quick and simplified inoculation of IC/MEMS. Since such a conventional biomolecule FET represents the SNR when actually performing a test, it has disadvantages of lowering reproducibility and precision.
FIG. 1A is a cross-sectional view of a conventional biomolecule FET. A source 12a and a drain 12b are formed on both sides of an n-type or p-type doped substrate 11. A gate 13 is formed on the substrate 11 to be in contact with the source 12a and the drain 12b. The gate 13 generally includes an oxide layer 14, a poly-silicon layer 15, and a gate electrode layer 16, and probe biomolecules are attached to the gate electrode layer 16. The probe biomolecules are coupled by a desired target biomolecule and hydrogen bond, and is detected using an electrical method to measure a coupling degree of the probe and the target biomolecule.
FIG. 1B shows a probe 18 attached to a surface of the gate electrode 16 and the target biomolecule coupled to the probe 18. According to the biomolecule FET using a reference electrode 17, there is a difference in electric potential between the source 12a and the reference electrode 17, and the drain 12b and the reference drain 17. Biomolecules charged by electrokinetic force under an electric field are not uniformly distributed on the gate 13 between the source 12a and the drain 12b, and the distribution is varied depending upon a position. For example, in DNA having a negative electric charge, when immobilization of a probe DNA and hybridization of a target DNA are detected using a p-type FET, the immobilization of a probe DNA and the hybridization of a target DNA are high on the gate 13 adjacent to the source 12a under the influence of a strong electric field between the source 12a and the reference electrode 17. Consequently, the charge density of the biomolecule attached to the surface of the gate 13 directly affects a variation of the FET current. Therefore, since the charge density on the gate 13 is varied depending upon the position, there is needed for a method of increasing the SNR of the biomolecule FET by altering the structure of the gate 13.